[RFC PATCH v2 06/29] ntsync: Introduce NTSYNC_IOC_CREATE_MUTEX.

Elizabeth Figura
2024-01-31T02:16:03Z

This corresponds to the NT syscall NtCreateMutant().

An NT mutex is recursive, with a 32-bit recursion counter. When acquired via
NtWaitForMultipleObjects(), the recursion counter is incremented by one.

The OS records the thread which acquired it. However, in order to keep this
driver self-contained, the owning thread ID is managed by user-space, and passed
as a parameter to all relevant ioctls.

The initial owner and recursion count, if any, are specified when the mutex is
created.

Signed-off-by: Elizabeth Figura <zfigura@codeweavers.com>
---
drivers/misc/ntsync.c | 67 +++++++++++++++++++++++++++++++++++++
include/uapi/linux/ntsync.h | 7 ++++
2 files changed, 74 insertions(+)

diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c
index b86d62094344..484219a266ae 100644
--- a/drivers/misc/ntsync.c
+++ b/drivers/misc/ntsync.c
@@ -17,6 +17,7 @@

enum ntsync_type {
NTSYNC_TYPE_SEM,
+ NTSYNC_TYPE_MUTEX,
};

struct ntsync_obj {
@@ -33,6 +34,10 @@ struct ntsync_obj {
__u32 count;
__u32 max;
} sem;
+ struct {
+ __u32 count;
+ __u32 owner;
+ } mutex;
} u;

/*
@@ -112,6 +117,10 @@ static bool is_signaled(struct ntsync_obj *obj, __u32 owner)
switch (obj->type) {
case NTSYNC_TYPE_SEM:
return !!obj->u.sem.count;
+ case NTSYNC_TYPE_MUTEX:
+ if (obj->u.mutex.owner && obj->u.mutex.owner != owner)
+ return false;
+ return obj->u.mutex.count < UINT_MAX;
}

WARN(1, "bad object type %#x\n", obj->type);
@@ -154,6 +163,10 @@ static void try_wake_all(struct ntsync_device *dev, struct ntsync_q *q,
case NTSYNC_TYPE_SEM:
obj->u.sem.count--;
break;
+ case NTSYNC_TYPE_MUTEX:
+ obj->u.mutex.count++;
+ obj->u.mutex.owner = q->owner;
+ break;
}
}
wake_up_process(q->task);
@@ -195,6 +208,28 @@ static void try_wake_any_sem(struct ntsync_obj *sem)
}
}

+static void try_wake_any_mutex(struct ntsync_obj *mutex)
+{
+ struct ntsync_q_entry *entry;
+
+ lockdep_assert_held(&mutex->lock);
+
+ list_for_each_entry(entry, &mutex->any_waiters, node) {
+ struct ntsync_q *q = entry->q;
+
+ if (mutex->u.mutex.count == UINT_MAX)
+ break;
+ if (mutex->u.mutex.owner && mutex->u.mutex.owner != q->owner)
+ continue;
+
+ if (atomic_cmpxchg(&q->signaled, -1, entry->index) == -1) {
+ mutex->u.mutex.count++;
+ mutex->u.mutex.owner = q->owner;
+ wake_up_process(q->task);
+ }
+ }
+}
+
/*
* Actually change the semaphore state, returning -EOVERFLOW if it is made
* invalid.
@@ -352,6 +387,33 @@ static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)
return put_user(fd, &user_args->sem);
}

+static int ntsync_create_mutex(struct ntsync_device *dev, void __user *argp)
+{
+ struct ntsync_mutex_args __user *user_args = argp;
+ struct ntsync_mutex_args args;
+ struct ntsync_obj *mutex;
+ int fd;
+
+ if (copy_from_user(&args, argp, sizeof(args)))
+ return -EFAULT;
+
+ if (!args.owner != !args.count)
+ return -EINVAL;
+
+ mutex = ntsync_alloc_obj(dev, NTSYNC_TYPE_MUTEX);
+ if (!mutex)
+ return -ENOMEM;
+ mutex->u.mutex.count = args.count;
+ mutex->u.mutex.owner = args.owner;
+ fd = ntsync_obj_get_fd(mutex);
+ if (fd < 0) {
+ kfree(mutex);
+ return fd;
+ }
+
+ return put_user(fd, &user_args->mutex);
+}
+
static struct ntsync_obj *get_obj(struct ntsync_device *dev, int fd)
{
struct file *file = fget(fd);
@@ -469,6 +531,9 @@ static void try_wake_any_obj(struct ntsync_obj *obj)
case NTSYNC_TYPE_SEM:
try_wake_any_sem(obj);
break;
+ case NTSYNC_TYPE_MUTEX:
+ try_wake_any_mutex(obj);
+ break;
}
}

@@ -661,6 +726,8 @@ static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
void __user *argp = (void __user *)parm;

switch (cmd) {
+ case NTSYNC_IOC_CREATE_MUTEX:
+ return ntsync_create_mutex(dev, argp);
case NTSYNC_IOC_CREATE_SEM:
return ntsync_create_sem(dev, argp);
case NTSYNC_IOC_WAIT_ALL:
diff --git a/include/uapi/linux/ntsync.h b/include/uapi/linux/ntsync.h
index 524404f6aceb..d68f24fd75a2 100644
--- a/include/uapi/linux/ntsync.h
+++ b/include/uapi/linux/ntsync.h
@@ -16,6 +16,12 @@ struct ntsync_sem_args {
__u32 max;
};

+struct ntsync_mutex_args {
+ __u32 mutex;
+ __u32 owner;
+ __u32 count;
+};
+
struct ntsync_wait_args {
__u64 timeout;
__u64 objs;
@@ -30,6 +36,7 @@ struct ntsync_wait_args {
#define NTSYNC_IOC_CREATE_SEM _IOWR('N', 0x80, struct ntsync_sem_args)
#define NTSYNC_IOC_WAIT_ANY _IOWR('N', 0x82, struct ntsync_wait_args)
#define NTSYNC_IOC_WAIT_ALL _IOWR('N', 0x83, struct ntsync_wait_args)
+#define NTSYNC_IOC_CREATE_MUTEX _IOWR('N', 0x84, struct ntsync_sem_args)

#define NTSYNC_IOC_SEM_POST _IOWR('N', 0x81, __u32)

--
2.43.0